Chronic Power Steering Problems on Early 2-Ton Truck

I have a GMC 6500 thats been converted over to a 454 gas engine. It had a 350 in it and when it was converted over and the old humongous power steering unit was tossed. The old unit had a huge reservoir. The standard one in it now is for 1 ton or smaller trucks.

Since that time Ive had chronic issues with the power steering. I replaced the pump, hoses and all with new. The only thing I didnt mess with is the steering gearbox.

The symptoms are that it works fine for the first few minutes of being full of fluid. But after about 10 minutes parked, I crank the wheel far left and right and fluid pressure builds up in the reservoir so bad that it spews out and then shortly thereafter stops assisting. I check the reservoir, engine off, and its half full by then. I refill with fluid and it starts all over again. I am fearful its the old steering gearbox cus thats what I simply cant afford to repair or replace. It doesnt seem to me that the reservoir size should really matter, and the new pump should work even IF its too small, and the fact that it was working well before the switch and seldom is the gearbox the problem rules that out too. Any other suggestions?

Is the current reservoir built into the pump like most older GM vehicles? Can’t you build some brackets so you can mount the original system to the new engine?

What sort of diameter difference is there between the new lines and the old? Is there a difference? I am thinking that maybe the truck’s steering box requires a larger volume of fluid than your current lines can handle. Just a thought.

If I thought the problem was possibly capacity related, I would make a one or two quart canister up with a couple of barbs on it.
Splice the canister into the return line since it’s a low pressure line and then see what happens with a lot more fluid available to the pump.

Just an idea anyway.

I like that last idea. I will unplug and attach it to a “T” going up to a second reservoir.

Before I go through the trouble however, Im going to blow-back through the gearbox with 90 psi air in hopes its not a simple debris problem.


P.S. To the other guy, I said the old pump was tossed. A replacement costs hundred$.